1. Field of the Invention
The present invention relates to a fuel cell formed by stacking electrolyte electrode assemblies and separators alternately in a horizontal direction. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes. A reactant gas flow field for supplying a reactant gas is formed between the electrode electrolyte assembly and one of separators sandwiching the electrolyte electrode assembly for supplying a reactant gas along a surface of the electrode, and a coolant flow field is formed between adjacent separators which are stacked together for allowing a coolant to flow in a direction substantially perpendicular to the flow direction of the reactant gas.
2. Description of the Related Art
For example, a polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes an anode, a cathode, and an electrolyte membrane (electrolyte) interposed between the anode and the cathode. The electrolyte membrane is a solid polymer ion exchange membrane. The membrane electrode assembly and separators sandwiching the membrane electrode assembly make up a unit of a power generation cell for generating electricity. Normally, a predetermined number of the power generation cells are stacked together alternately to form a fuel cell stack.
In the power generation cell, a fuel gas flow field (reactant gas flow field) for supplying a fuel gas along the surface of the anode and an oxygen-containing gas flow field (reactant gas flow field) for supplying an oxygen-containing gas along the surface of the cathode are formed on a pair of separators sandwiching the membrane electrode assembly. Further, a coolant flow field for cooling the power generation surfaces of the membrane electrode assembly is formed between the adjacent separators which are stacked together.
For example, U.S. Pat. No. 5,547,776 discloses an electrochemical fuel cell having an oxygen-containing gas/coolant flow field plate 1 as shown in FIG. 10. The plate 1 has an oxygen-containing gas supply passage 2a and an oxygen-containing gas discharge passage 2b at two diagonal corners, and a fuel gas supply passage 3a, a coolant discharge passage 4b, a fuel gas discharge passage 3b, and a coolant supply passage 4a at the other two diagonal corners.
An oxygen-containing gas flow field 5 comprising a plurality of grooves in a serpentine pattern is formed on one surface of the plate 1, along the power generation reaction area. The oxygen-containing gas flow field 5 is connected to the oxygen-containing gas supply passage 2a and the oxygen-containing gas discharge passage 2b. 
A coolant flow field (not shown) is formed on the other surface of the plate 1. The coolant flow field is connected to the coolant supply passage 4a and the coolant discharge passage 4b. As with the oxygen-containing gas flow field 5, the coolant flow field comprises a plurality of grooves in a serpentine pattern. In the coolant flow field, the temperature is the lowest at a position corresponding to the area of the oxygen-containing gas flow field 5 where the amount of water is the smallest, while the temperature is highest at a position corresponding to the oxygen-containing gas flow field 5 where the amount of water is the largest.
However, in the conventional technique, the oxygen-containing gas flow field 5 and the coolant flow field are formed on both surfaces of the plate 1. The flow grooves of the oxygen-containing gas flow field 5 and the flow grooves of the coolant flow field have substantially the same shape in the serpentine pattern, for example. Thus, the shape of the oxygen-containing gas flow field 5 and the shape of the coolant flow field need to be substantially the same.
That is, the shapes of the flow fields cannot be designed freely. For example, grooves of reactant gas flow fields (e.g., the oxygen-containing gas flow field 5) cannot be formed in substantially perpendicular to the grooves of the coolant flow field. In such a structure, the fuel cell cannot be used in a variety of applications.